This invention relates to fire retardant compositions which are specially adapted for aerial application, to combat or prevent the spread of wildfires.
More particularly, the invention concerns a fugitive color fire retardant composition, having improved aerial visibility after it is first aerially applied to ground vegetation, but which fades over time and under ambient conditions to another color (hue).
In the early 1960""s aerial application of fire retardant compositions, to prevent or retard the spread of forest fires, range fires, etc., became very widespread. Typically, these fire retardant compositions contained an electrolytic fire suppressing salt such as ammonium phosphate, ammonium sulfate, and the like and also included other components such as viscosity modifiers, corrosion inhibitors and coloring agents such as pigments or dyes. Typical fire retardant compositions of the type described above are disclosed in the patents to Nelson, U.S. Pat. No. 3,196,108, and to Langguth et al., U.S. Pat. Nos. 3,257,316 and 3,309,324. These compositions generally consisted of an aqueous slurry or solution of a fire suppressing salt such as ammonium phosphate or ammonium sulfate and a thickening agent such as attapulgite clay, guar gum or the like. Coloring agents such as red iron oxide were included to improve the visibility of the material after it was dropped. More recently, ammonium polyphosphate liquids, containing coloring agents and corrosion inhibitors, have been widely employed. Such liquid polyphosphate fire retardant compositions are disclosed in the patents to Nelson, U.S. Pat. No. 3,370,890 and to Lacey, U.S. Pat. No. 3,960,735.
Fire retardant compositions containing other thickeners, stabilizers and the like are disclosed in the patents to Strickland, U.S. Pat. No. 4,822,524; Morganthaler, U.S. Pat. No. 3,634,234; Kegler et al., U.S. Pat. No. 4,606,831; Vandersall, U.S. Pat. No. 4,447,336; Adl et al., U.S. Pat. No. 4,447,338; and Vandersall, U.S. Pat. Nos. 4,839,065 and 4,983,326.
Fire retardant compositions are typically manufactured as dry or liquid xe2x80x9cconcentratesxe2x80x9d. These concentrates are shipped and stored in such form until just prior to use. Then, the concentrate is mixed with water to form the final diluted xe2x80x9cmixedxe2x80x9d fire retardant composition. This mixed retardant composition is then pumped in the tanker aircraft for transport to and dropping at the wildfire site. In some instances a dry concentrate is first mixed with an initial quantity of water to provide an intermediate liquid concentrate and this intermediate liquid concentrate is then further diluted just before use to the final diluted mixed form.
The active fire suppressing components employed in such retardant compositions include any of the well known electrolytic fire suppressing salts, e.g., such as are disclosed in the patent to Nelson U.S. Pat. No. 3,196,108, as well as the more recently employed liquid ammonium polyphosphate materials, as disclosed in the patent to Lacey U.S. Pat. No. 3,960,735; ammonium sulfate, as disclosed in the patent to Crouch U.S. Pat. No. 4,176,071; and mixtures of these salts with themselves and with other salts.
In general, the active fire retardant components are compounds or a mixture of compounds that degrade or decompose at temperatures below the ignition temperature of the fuels to be protected (e.g., cellulose), thereby releasing a mineral acid, such as phosphoric acid or sulfuric acid. Among the various fire retardants typically used in fire retardant mixtures and which might be used in the compositions of this invention are monoammonium orthophosphate, diammonium orthophosphate, monoammonium pyrophosphate, diammonium pyrophosphate, triammonium pyrophosphate, tetraammonium pyrophosphate, ammonium polyphosphate, substituted ammonium polyphosphate, amide polyphosphate, melamine polyphosphate, ammonium-alkali metal mixed salts of orthophosphate, ammonium-alkali metal mixed salts of pyrophosphate, ammonium-alkali metal mixed salts of polyphosphate, ammonium-alkaline earth metal mixed salts of orthophosphate, ammonium-alkaline earth metal mixed salts of pyrophosphate, ammonium-alkaline earth metal mixed salts of polyphosphate, ammonium sulfate, liquid ammonium polyphosphates and blends thereof. Some liquid ammonium polyphosphates may be too dilute in their commercial forms for application as fire retardants but, other retardants, such as those noted above, may be mixed with a liquid ammonium polyphosphate until a minimum acceptable concentration is obtained. Ammonium polyphosphate is-often called polyammonium phosphate, and commonly contains other ammonium phosphate such as pyro and metaphosphates, and the alkali metal equivalents thereof, as well as a blend of phosphate polymers. Such polyammonium phosphates are often referred to as 10-34-0, 11-37-0, 12-40-0, 13-42-0 or the like, where the first number indicates the percentage of nitrogen in the blend, the middle number indicates the percentage phosphate in the blend and the last number indicates the percentage potash in the blend.
The fire retardant components may also include thickening agents, which include standard thickeners such as galactomannan guar gum compositions and derivatives thereof attapulgite clay, carboxymethylcellulose and derivatives thereof, and the like. The thickening agent is employed to maintain the viscosity of the diluted mixed fire retardant composition, for example, at between about 50 centipoise and about 2000 centipoise for aerial application. In addition, the fire retardant components, in the concentrate or in the final diluted mixed form, may also typically include various adjuvants such as corrosion inhibitors, flow conditioners, spoilage inhibitors, stabilizers and the like, and carriers for these adjuvants, in accordance with art recognized principles.
When such fire retardant compositions, in final diluted mixed form for aerial application, are applied by dropping from fixed-wing or helicopter aircraft, successive xe2x80x9cdropsxe2x80x9d are often made by the aircraft to form a fire-fighting line. Under these circumstances, it is important for the pilot of the aircraft to be able to visually determine where the preceding loads were dropped, such that the pilot can drop the load from the aircraft to form a continuation of this line. Since the fire retardant components (described above) may be colorless or may be of colors which do not contrast well with the ground or vegetation, it has been common practice to mix coloring agents with the fire retardant composition components. Coloring agents are used to give the fire retardant compositions a color (hue) which contrasts with the hue of the ground vegetation, thereby enhancing the ability of the aircraft pilot to determine where the last loads of fire retardants were dropped in constructing a fire-fighting line. Prior art coloring agents have included pigments which are dispersible in the liquid fire retardant compositions or soluble therein, most commonly red iron oxide or various water soluble dyes. Such coloring agents were remarkably effective in enhancing the aerial visibility of fire retardant compositions after they were applied. However, certain prior art coloring agents, especially red iron oxide, were very xe2x80x9ccolorfastxe2x80x9d, such that the ground and structures (if any) to which the prior art fire retardant compositions were applied, remained permanently or semi-permanently stained. Consequently, certain government fire-fighting agencies have, more recently, required that aerially applied fire retardant compositions have so-called xe2x80x9cfugitivexe2x80x9d coloring agents, such that the color of the compositions would fade over a short time, e.g., 30 days, to a color which did not objectionably contrast with the ground and ground vegetation.
Several dyes and pigments (encapsulated dyes) have been identified which impart a distinctive hue to fire retardant compositions, which contrasts with ground vegetation, but which allow the fire retardant compositions to fade in a short time to a xe2x80x9cneutralxe2x80x9d color, i.e., the color the fire retardant compositions would have exhibited without the addition of such fugitive agents which may be colorless or a color which blends with the natural color of the vegetation and/or ground in the drop zone. However, although the fire retardant compositions themselves might be brilliantly colored by fugitive agents, after first application it was often difficult to locate the fire retardant drop zone. It has been found that the reduced visibility of these highly colored fugitive compositions is somewhat related to the viscosity of the fire retardant compositions themselves. Thus, more highly viscous fugitive compositions are somewhat easier to see on the vegetation, because they form a thicker coating. However, even highly viscous fugitive color compositions are sometimes difficult to visualize from an aircraft after dropping on various kinds of vegetation and under various lighting conditions.
It would be advantageous to provide fugitive color fire retardant compositions which exhibit improved aerial visibility after dropping. It would also be advantageous to achieve this result in an economical manner and without using any materials which are toxic to humans, animals, fish or to vegetation.
Briefly, we have discovered a fugitive color liquid fire retardant composition for aerial application to ground vegetation which achieves these objectives. Our composition comprises fire retardant components, a colorant and a liquid carrier, typically an aqueous carrier. The colorant comprises a fugitive component and a non-fugitive component. The fire retardant components and the non-fugitive components have a first hue which is a color, i.e., either colorless or a color which blends with the normal vegetation and/or ground in the drop zone.
The colorant initially colors the fire retardant composition components to a second hue which contrasts with the hue of the ground vegetation. This may be due solely to the color imparted by the fugitive component or the color imparted by the combined fugitive/non-fugitive components.
The non-fugitive component of our colorant is present in an amount sufficient to improve the aerial visibility of the composition when it is first applied to the vegetation. However, the non-fugitive component is present in less than an amount which prevents the composition from thereafter fading a neutral color.
According to another embodiment of our invention, we provide a concentrate composition for preparing the liquid composition described above by dilution thereof with the aqueous carrier. The concentrate composition comprises the fire retardant components and the colorant and may include at least part of the liquid carrier.
In one embodiment, the concentrate is a dry composition. In another embodiment the concentrate is a liquid, suitable for later dilution with water to form the final mixed liquid fire retardant composition.
According to yet another embodiment of the invention, we provide an improved method for fighting wild fires, including the step of aerially applying a fire retardant composition, which includes fire retardant components, comprising a fire retarding salt, a fugitive color component, and further including a liquid carrier. Our improved method increases the aerial visibility of the fire retardant composition after aerial application and includes the step of incorporating a non-fugitive component into the fire retardant composition, before it is aerially applied. A sufficient amount of the non-fugitive component is added to increase the aerial visibility of the composition, but less than an amount which prevents the composition from fading, after application, to a neutral hue.